Enjoyed having nitrogen to waste (4)
I believe the answer is:
dung
'to waste' is the definition.
(dung is a kind of waste)
'enjoyed having nitrogen' is the wordplay.
'enjoyed' becomes 'dug' (slang).
'having' indicates putting letters inside.
'nitrogen' becomes 'N' (N is the chemical symbol for nitrogen).
'dug' going around 'n' is 'DUNG'.
(Other definitions for dung that I've seen before include "Animal excrement" , "Animal manure" .)